Use RegExp to restrict input data - javascript

I try to force the user to enter a password with exact number of caracts.
The password have to be like that :
8 total caracts :
1 (exactly) uppercase,
3 (exactly) numbers
and lowercases (4 in that case).
The regex i have : (?=.*[a-z])(?=.*[A-Z]{1})(?=.*[0-9]{3})
The problem is we can put more than 3 numb and more then 1 uper and more than 8 caract..
Examples :
5p23qPsb -> OK
I9Opdi90 -> NOT OK
h7y1Rdw6 -> OK
IUD8954r -> NOT OK
An idea or some help ?
Thanks (I'm french so sorry for my english..)

You are definitely on the right track with this. You are stacking lookaheads, but lookaheads don't actually match anything. They just check to make sure that it can complete a match. So you'll need to add something like a .+ for it to actually match on. Here is a workdown on how you can validate your string.
Let's start with the entire string. We want it to be exactly 8 characters, so we can do something like this:
^(?=.{8}$)
Then, we want exactly one uppercase letter, so we can make a lookahead like this:
(?=.*[A-Z])
Next, we want to require exactly one digit, so we can use this:
(?=.*[0-9])
Finally, we want to require exactly 4 lowercase letters that may or may not be next to each other. Here's a lookahead that matches that:
(?=.*[a-z].*[a-z].*[a-z].*[a-z])
Now that we've got all of the pieces, we can set our actual expression to match any character, more than one time .+. The previous lookaheads will make sure it fits the requirements. Piecing everything together, we end up with an expression like this:
^(?=.{8}$)(?=.*[a-z].*[a-z].*[a-z].*[a-z])(?=.*[A-Z])(?=.*[0-9]).+
Here is a demo

/(?=.*?[A-Z]{1})(?=.*?[a-z]{4})(?=.*?[0-9]{3})/.test("123Aacds");

Related

Regex: Comma separated values

I have been trying to make a regex that will: match only if all condition are met, will not match 1 to 10 or something like it and will ignore commas.
I have made (?=.*1)(?=.*5) which almost works and will match to 1,5 as it is meant to but will also match to 10,5,10,50 and 1,50. I can not work out how to stop this. So my question is how do I get the regex to know the difference between numerals and a single digit.
Make it match word boundaries around the number, using \b.
(?=.*\b1\b)(?=.*\b5\b)

Javascript RegEx - Enforcing two max-lengths

It's been a while that I am juggling around this. Hope you can give me
some pointers.
All I want to achieve is, the string should contain EXACTLY 4 '-' and 10 digits in any giver order.
I created this regex : ^(-\d-){10}$
It does enforce max-length of 10 on digits but I am not getting a way to implement max-length of 4 for '-'
Thanks
Ok, here's a pattern:
^(?=(?:\d*?-){4}\d*$)(?=(?:-*?\d){10}-*$).{14}$
Demo
Explanation:
The main part is ^.{14}$ which simply checks there are 14 characters in the string.
Then, there are two lookaheads at the start:
(?=(?:\d*?-){4}\d*$)
(?=(?:-*?\d){10}-*$)
The first one checks the hyphens, and the second one checks the digits and make sure the count is correct. Both match the entire input string and are very similar so let's just take a look at the first one.
(?:\d*?-){4} matches any number of digits (or none) followed by a hyphen, four times. After this match, we know there are four hyphens. (I used an ungreedy quantifier (*?) just to prevent useless backtracking, as an optimization)
\d*$ just makes sure the rest of the string is only made of digits.

Matching multiple optional characters depending on each other

I want to match all valid prefixes of substitute followed by other characters, so that
sub/abc/def matches the sub part.
substitute/abc/def matches the substitute part.
subt/abc/def either doesn't match or only matches the sub part, not the t.
My current Regex is /^s(u(b(s(t(i(t(u(te?)?)?)?)?)?)?)?)?/, which works, however this seems a bit verbose.
Is there any better (as in, less verbose) way to do this?
This would do like the same as you mentioned in your question.
^s(?:ubstitute|ubstitut|ubstitu|ubstit|ubsti|ubst|ubs|ub|u)?
The above regex will always try to match the large possible word. So at first it checks for substitute, if it finds any then it will do matching else it jumps to next pattern ie, substitut , likewise it goes on upto u.
DEMO 1 DEMO 2
you could use a two-step regex
find first word of subject by using this simple pattern ^(\w+)
use the extracted word from step 1 as your regex pattern e.g. ^subs against the word substitute

Javascript regex: is there anyway to write a regex which gives true if backreference is NOT matched

so here is my problem: I'm checking an input of 2 years with a hyphen. Like:
2001-2015
To test this, I use the simple regex
/^([0-9]{4})-([0-9]{4})$/
I know groups aren't needed, and (19|20)[0-9]{2}, is a closer match to the basic year exp, but bear with me.
Now, if my requirement was to match the two years only if they are the same, i could have used a backreference like:
/^([0-9]{4})-\1$/
which matches 2000-2000 but not 2000-2014
My actual requirement is exactly the opposite. I want it to match if the years are different but not if they're same. That is, 2000-2014 should match. 2000-2000 should not.
And using the negative of the boolean I find is not an option. I need this for a huuuge regex which is supposed to match a whole lot of different date formats. This is just a part of it.
Is there any way to achieve this?
You can use a negative lookahead to achieve this:
^([0-9]{4})-(?!\1)[0-9]{4}$
Demo
This is almost the same pattern, except it inserts a condition check using the backreference.
(?!\1) will fail if \1 matches at its position.
You can use negative lookahead:
\b(\d{4})-(?!\1)\d{4}\b
RegEx Demo
Use Negative Lookahead.
Like this :
^([0-9]{4})-(?!\1)[0-9]{4}$
It does work on your example.
Explanation : (?!\1) Assert that it is impossible to match the regex \1. Then you just put your 4 digits requirement.

UK bank sort code javascript regular expression

I'm trying to create a regular expression in javascript for a UK bank sort code so that the user can input 6 digits, or 6 digits with a hyphen between pairs. For example "123456" or "12-34-56". Also not all of the digits can be 0.
So far I've got /(?!0{2}(-?0{2}){2})(\d{2}(-\d{2}){2})|(\d{6})/ and this jsFiddle to test.
This is my first regular expression so I'm not sure I'm doing it right. The test for 6 0-digits should fail and I thought the -? optional hyphen in the lookahead would cause it to treat it the same as 6 0-digits with hyphens, but it isn't.
I'd appreciate some help and any criticism if I'm doing it completely incorrectly!
Just to answer your question, you can validate user input with:
/^(?!(?:0{6}|00-00-00))(?:\d{6}|\d\d-\d\d-\d\d)$/.test(inputString)
It will strictly match only input in the form XX-XX-XX or XXXXXX where X are digits, and will exclude 00-00-00, 000000 along with any other cases (e.g. XX-XXXX or XXXX-XX).
However, in my opinion, as stated in other comments, I think it is still better if you force user to either always enter the hyphen, or none at all. Being extra strict when dealing with anything related to money saves (unknown) troubles later.
Since any of the digits can be zero, but not all at once, you should treat the one case where they are all zero as a single, special case.
You are checking for two digits (\d{2}), then an optional hyphen (-?), then another two digits (\d{2}) and another optional hyphen (-?), before another two digits (\d{2}).
Putting this together gives \d{2}-?\d{2}-?\d{2}, but you can simplify this further:
(\d{2}-?){2}\d{2}
You then use the following pseudocode to match the format but not 000000 or 00-00-00:
if (string.match("/(\d{2}-?){2}\d{2}/") && !string.match("/(00-?){2}00/"))
//then it's a valid code, you could also use (0{2}-?){2}0{2} to check zeros
You may wish to add the string anchors ^ (start) and $ (end) to check the entire string.

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